A hearing device is used to improve the hearing of a hearing impaired person in that surrounding sound is picked-up by a microphone. The sound signal is processed taking into account the hearing impairment in order to obtain a processed sound signal that allows the hearing device user to have an improved hearing. In particular hearing device components exposed to the surrounding are subject to wear. Such components are, for example, microphone protections, microphones themselves, receivers and tubing systems. Due to the exposure to the surrounding, these components may become dirty or even stop working due to the dirt or due to mechanical stress, for example, from falling to the floor. Thus, hearing devices must be tested regularly in order to function reliably.
Classically, the functioning of a hearing device is checked by holding it in a closed hand. If it starts whistling, everything is assumed to work correctly. This is a rather crude self test though, and does not allow identifying any specific problem.
Self tests have already been proposed to check some of the components of a hearing device. Most of these known teachings use a box with a defined acoustic path between receiver and microphone of the hearing device. Reference is made to the teachings described in EP-1 865 746 A2, DE-103 54 897 A1, U.S. Pat. No. 6,671,643 B2, and US-2008/0 253 579 A1. The box may be the one, in which the hearing device has been bought, or, a box that has to be purchased by the hearing device user as an accessory. In any case, the box must be available to perform the test, which is perceived as disadvantage by the hearing device user because the box is very often not available or cannot be found when needed. Furthermore, the manufacturer of the hearing device must have a stock of boxes to be able to provide replacement boxes for the hearing device user. As a result thereof, the production costs for such hearing devices increase.
Another known teaching discloses a hearing device with an internal signal generator that allows generating a test sound signal which is picked up by the microphone and tested internally. In this connection, reference is made to U.S. Pat. No. 6,792,114 B1 and to EP-1 276 349 B1. The known teachings have both the disadvantage that the acoustic path is not well defined between receiver and microphone, thus an attenuation that is due to a dirty microphone protection, for example, is not reliably detectable.
Furthermore, all methods, which use an internal signal generator to measure the signal path towards the microphone of the hearing device lack of the problem that they cannot easily distinguish, if an attenuation is caused by a dirty microphone protection or a dirty receiver/wax guard, or if one or the other is broken as both lie in the same signal path. This is even the case when the acoustic signal path between the receiver and the microphone of the hearing device is completely incorporated into a box.
It is therefore an object of the present invention to provide an easy and cheap method for testing a hearing device that does at least not have some of the disadvantages of the prior art.